JP2003273504A - Soldering method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simplified method to additionally supply an oxidation control element to solder bath not using a mother alloy of higher oxidation control element concentration. <P>SOLUTION: A solder alloy including the oxidation control element of an amount larger than the reduction amount thereof obtained from reduction rate is additionally supplied depending on the reduction amount of solder bath by measuring the reduction rate of the oxidation control element in the solder bath used. Composition of the solder alloy is always held to a constant value as accurately as possible. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a soldering method,
In particular, it relates to a soldering method which is performed while controlling the concentration of the oxide suppressing element in the solder bath.

[0002]

2. Description of the Related Art Solder alloys are used to mount electronic components on printed wiring boards in electronic devices, and heat effects and work on electronic components and printed wiring boards (hereinafter also simply referred to as printed wiring boards). Solder alloys having various compositions are used in consideration of the reliability and the reliability after joining.

The solder alloys that have been widely used in the past are solder alloys having a composition near Sn-Pb eutectic (Sn63-Pb) having a low melting point and good solderability. Since this eutectic solder has no melting temperature range and instantly solidifies, it takes a short time to solidify after soldering. Therefore, in the soldering by the flow soldering method using the Sn-Pb eutectic solder, it is possible to perform highly reliable soldering in which the influence of vibration during conveyor transportation is very small.

However, Sn which is excellent in practical use
-Pb solder alloy is a lead-free solder from the point of pollution problem,
In other words, solder alloys that do not contain lead are being replaced. When acid rain comes into contact with the soldered part of an electronic device that is to be landfilled, Pb in the solder alloy will elute, which may lead to lead poisoning in the human body when contaminating groundwater and making it for drinking. It is due to the fact.

Here, the lead-free solder is superior in mechanical strength to the Sn-Pb solder, and in consideration of the above-mentioned problem of lead pollution, it has recently come to be widely used. There is.

As a soldering method using these solder alloys, a flow soldering method using a molten solder bath, a reflow method using a solder paste or a foam solder, and a trowel method for soldering a greasy wire solder with a trowel There are laws etc.

In the flow soldering method, after flux is applied to the entire area of one surface of a printed circuit board on which electronic parts are mounted,
In this method, one side of a printed circuit board is brought into contact with a molten solder bath after preheating and then soldering is performed.
In this method, in recent years, the molten solder is jetted using a nozzle to generate a stable molten solder wave, and the wave soldering method of passing the substrate so that it hits the top of the wave soldering method as a printed circuit board mounting method.
It is common for cost-oriented mass production.

By the way, during the soldering work, some soldering defects, that is, unsoldered solder, bridges, voids, etc. occur. Especially in the flow soldering method,
Since the solder is constantly jetted, the solder flowing out from the jet nozzle drops to the stationary part in the bath near the nozzle. Turbulent flow occurs in this falling portion, and oxides due to oxygen entrapment, so-called dross, is generated. If dross accumulates near the nozzle, it may impair the stability of the molten solder wave, or part of the dross caught in the solder wave may adhere to the printed circuit board, resulting in soldering defects. It is necessary to regularly remove the accumulated dross.

The same problem of dross generation occurs when high temperature soldering is performed in an oxidizing atmosphere, such as when soldering urethane-coated copper wires, even when using a static solder bath. Can be seen.

If such a large amount of dross is generated, the labor required for removing the dross and the amount of waste solder are increased, and the running cost is increased. Therefore, it is desired to reduce this dross in terms of maintenance and cost of the solder bath.

Since the material itself of lead-free solder is expensive, further reduction of dross is strongly demanded. In order to reduce this dross, a deoxidizing alloy to which an element having an effect of suppressing oxidation is added has been used as a solution from the solder alloy side. A typical example of the oxidation suppressing element is P. P has an effect of suppressing the oxidation of Sn or Pb, which is a main constituent of the solder alloy, by positively reacting with oxygen.

The effect of suppressing the oxidation of P is so-called sacrificial oxidation, which eventually leads to the suppression of dross. P is selectively consumed and concentrated in the dross, and is discharged out of the solder bath together with the dross. Therefore, P in the solder alloy, that is, the oxidation inhibiting element, decreases and eventually disappears.

When the oxidation suppressing element in the solder alloy disappears, the dross suppressing effect is lost, so that the amount of dross generated increases, not only the amount of waste solder increases, but also soldering defects due to dross occur, There is a possibility that the total defective rate associated with the flow soldering may increase and the running cost may increase.

In the conventional method of adding an oxidation inhibiting element to a solder bath, a small amount of a solder alloy (P: 0.05 to 3%) having a P concentration extremely higher than a predetermined P concentration in the solder bath is used for deoxidation. It was a thing. (Reference: Japanese Patent Laid-Open No. 54-84817) In other words, in the past, when the P concentration in the solder bath decreased, a small amount of a solder alloy having a high P concentration was added, so that only the P concentration in the solder bath was increased. Was to recover.

On the other hand, when a large number of printed circuit boards are soldered, the solder alloy in the solder bath adheres to the printed circuit boards and is consumed. Conventionally, the supply of the reduced amount of solder in the solder bath has been performed with a solder alloy containing no P. That is, a small amount of a solder alloy having a high P concentration was added to reduce the amount of P in the solder bath, and a solder alloy containing no P was supplied to reduce the amount of solder alloy in the solder bath. Of. The P concentration in the solder bath and the amount of solder alloy were controlled separately.

Even when the P-containing solder is supplied to reduce the amount of the solder alloy in the solder bath, the solder alloy having the same concentration as that of the solder alloy previously filled in the solder bath was used. . In the case of the flow soldering method, particularly in the wave soldering method, since the amount of P consumed in the solder bath is large, it is necessary to supply P when the solder alloy having the same P amount as the solder bath is supplied.
The amount of P corresponding to the consumed amount could not be replenished.

Therefore, similarly to the above, in order to reduce the P content in the solder bath, a small amount of a solder alloy having a high P content was added to recover the P content in the solder bath.

[0018]

[Patent Document 1] Japanese Patent Application Laid-Open No. 54-84817
Top right column, lines 1-6

[Patent Document 2] Japanese Patent Application Laid-Open No. 11-333589 claims 3, 4

[0019]

Certainly, even in the conventional case, when the oxidation inhibiting element in the solder bath disappears, as described above, the amount corresponding to the consumption of the oxidation inhibiting element should be supplied. Has adopted a method to deal with. For example, it is a work of supplying the deoxidizing alloy in which the concentration of the oxidation inhibiting element is adjusted to a high concentration regularly every day or twice to four times a month into the solder bath to adjust the concentration of the oxidation inhibiting element in the bath.

However, each time the adjustment work is performed,
It was a troublesome work such as weighing the amount of the deoxidizing alloy to be blended, feeding it into the tank and stirring for a certain period of time, and confirming the concentration in the tank after adjustment.

An object of the present invention is to provide a soldering method for suppressing the oxidation of the solder alloy in the solder bath when the oxidation of the solder alloy in the solder bath poses a problem as in the flow soldering method. To do.

[0022]

[Means for Solving the Problems] By the way, in the flow soldering method, there are a portion that adheres to a printed circuit board during soldering and a portion that a dross portion generated by a jet flow is discharged outside the solder bath. The solder corresponding to the total discharge amount is supplied into the solder bath.

As the supply means, granular, rod-shaped solder or linear solder is used, and is supplied intermittently while controlling the liquid level in the solder bath. Therefore, in the past, when supplying a solder alloy having the same composition as the initial composition, the amount of the solder discharged, that is, the oxidation suppressing element was supplied at the same ratio as the initial composition in accordance with the supplied amount. is there.

Here, considering the sacrificial oxidation of P described above, the inventors of the present invention compared with the reduction ratio of the solder bath,
The reduction rate of the oxidation inhibiting element such as P is large, the large variation of P has a great influence on the mechanical properties of the solder joint, and the oxidation amount of the oxidation inhibiting element, that is, when the working conditions of soldering are constant, that is, The present invention has been completed as a result of further studies focusing on the fact that the reduction amount becomes relatively constant.

Further, if the oxidation inhibiting element is supplied in the form of a P-containing deoxidizing alloy at an appropriate time as in the conventional case, the composition of the solder bath changes, and accordingly, the reduction amount of the oxidation inhibiting element also largely changes. . Therefore, in the present invention,
By using a solder alloy with the same composition as the initial composition of the solder alloy as the solder alloy for supply, except for the oxidation inhibiting element and copper if necessary, even if the additional input time is determined by the decrease amount of the solder alloy, the solder bath composition The fluctuation of can be minimized.

The present invention is as follows. (1) A soldering method performed by using a solder bath to which an oxidation suppressing element is added, the solder having the same alloy composition as the alloy composition of the solder bath except the oxidation suppressing element and containing the oxidation suppressing element Using the alloy as a solder alloy for supply; determining the rate of decrease of the oxidation inhibiting element in the solder bath during the soldering operation; and reducing the amount of the oxidation inhibiting element consumed at the rate of decrease equal to or greater than Supplying a quantity of the oxidation-suppressing element to the solder bath as the supply solder alloy proceeds as a solder alloy for supplying; and a concentration of the oxidation-suppressing element in the solder bath. A soldering method characterized in that soldering is carried out while controlling within a predetermined range.

(2) A soldering method performed by using a solder bath to which an oxidation inhibiting element is added, wherein the solder alloy constituting the solder bath is a lead-free solder alloy containing copper as an alloy component. Using a solder alloy having the same alloy composition as that of the solder bath and containing the oxidation inhibiting element as a solder alloy for supply, except for the oxidation inhibiting element and copper; Determining the reduction rate of the oxidation inhibiting element; and supplying solder that supplies the oxidation inhibiting element in an amount equal to or greater than the reduction amount of the oxidation inhibiting element consumed at the reduction rate, and containing or not containing copper. And supplying the alloy to the solder bath as the supply solder alloy progresses as the soldering work progresses; the concentration of the oxidation inhibiting element in the solder bath is within a predetermined range. A soldering method characterized in that the soldering is carried out while controlling it.

(3) The oxidation inhibiting element in the supply solder alloy is contained in a concentration of 2 to 6 times the target concentration of the oxidation inhibiting element in the solder bath.
The soldering method described in (1) or (2) above.

(4) The oxidation inhibiting element is P, Ge, Ga, Ce
The soldering method according to any one of (1) to (3) above, which is one or more elements selected from
In the present invention, the supply solder alloy supplied into the solder bath may be supplied in the form of granular, rod-shaped or linear solder alloy.

According to the present invention, by simply adding the above-mentioned supply solder alloy in accordance with the decrease in the solder bath, the conventional deoxidizing alloy in which the oxidation suppressing element is adjusted to a high concentration is supplied into the solder bath. However, the troublesome work of adjusting the concentration in the tank can be omitted, and the oxidation suppressing element in the tank is automatically kept constant during daily normal work, and maintenance-free permanent use of the oxidation suppressing element is possible. Management can be achieved. By this method, it is possible to avoid the loss of the oxidation suppressing element in the solder bath and to permanently maintain the dross suppressing effect.
It is possible to secure stable soldering quality in flow soldering.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the oxidation inhibiting element used in the supply solder alloy is an element having an effect of inhibiting the oxidation of the main constituent components of the solder alloy by positively reacting with oxygen. The oxidation suppressing element is, for example, an element such as P, Ga, Ge or Ce.

The present invention is a flow soldering method using a solder bath, in which the content of the oxidation inhibiting element in the solder bath is kept as constant as possible while supplying the solder to the solder bath. That is, the present invention, in its broadest sense, is a method of soldering using a solder bath containing an oxidation inhibiting element, by supplying a solder alloy for supply to the solder bath, the progress of soldering Along with replenishing the solder bath that decreases with, consisting of compensating the consumption of the oxidation inhibiting element, the alloy composition of the solder alloy for supply has the same alloy composition except the oxidation inhibiting element. Further, the solder alloy for supply is a soldering method characterized in that the oxidation suppressing element is supplied to a solder bath in an amount equal to or more than the consumption amount.

Therefore, the elements of the solder in the solder bath and the elements of the solder alloy supplied to the solder bath are basically the same, but increase if the content of the elements increases during soldering. Solder containing no element or less than the prescribed content may be supplied. For example, the solder alloy that constitutes the solder bath in the solder bath is Sn
-In the case of Ag-Cu-P, when a large number of printed circuit boards are soldered with this solder, Cu gradually dissolves from the land of the printed circuit boards into the solder bath, and the Cu content of the solder bath is the specified content. More than the amount. As a result, needle-like CuSn intermetallic compounds are precipitated in the solder bath to short-circuit the soldered portions, or the liquidus temperature is raised to deteriorate the solderability.

In this way, when soldering
When Cu is increased, the solder alloy supplied to the solder bath should be a solder alloy containing no Cu or less than a predetermined Cu content. Also in this case, the oxidation suppressing element is a high-concentration solder alloy that can keep a predetermined concentration by following the reduction rate.

The solder alloy to which the present invention is applicable includes
Any solder alloy may be used as long as it is filled in a solder bath to form a solder bath and can be subjected to flow soldering. For example, in addition to the Sn-Pb solder alloys that have been used conventionally, lead-free solder alloys containing Sn as the main component (Sn-Ag, Sn-A
g-Cu, Sn-Cu, Sn-Bi, Sn-Zn). To these solder alloys, one or more of Ni, Co, Fe, Cr, Mo, etc., is added as a strength improving element, and further, Bi, I are added as melting point lowering elements.
It is also possible to add one or more of n, Zn and the like.

The operating procedure in each embodiment of the present invention is as follows. That is, according to the present invention,
Using a solder alloy having the same alloy composition except for the oxidation inhibiting element, an amount commensurate with the consumption of the oxidation inhibiting element is supplied to the solder bath in the following mode.

A solder alloy in which an oxidation inhibiting element is mixed in a predetermined concentration is melted and filled in a solder bath to form a solder bath. The operation of the solder bath with the soldering work for about 1 to 2 weeks is performed, and the reduction rate of the oxidation inhibiting element in the solder bath is grasped.

By grasping the reduction amount of the oxidation inhibiting element up to the time of charging, the supply amount corresponding to that is calculated. Grasp the amount of decrease in the solder alloy in the solder bath, determine the supply amount of the solder alloy of the amount that compensates for it, determine the concentration of the oxidation inhibiting element for it, and determine the oxidation inhibiting element equal to or higher than the concentration. A supply solder alloy is prepared that includes the others and is otherwise identical to the original composition of the solder alloy.

During operation of the solder bath, the supply solder alloy prepared when the solder alloy in the solder bath has decreased is supplied to the solder bath, and the concentration of the oxidation inhibiting element in the bath is adjusted to a predetermined concentration range (concentration set in ( To recover).

As a modified example of the present invention, there are the following aspects. This aspect relates to the case where the solder alloy contains copper, and using a solder alloy having the same alloy composition except for the oxidation inhibiting element and copper, an amount commensurate with the consumption of the oxidation inhibiting element is soldered in the following manner. Supply to the bath.

Oxidation-inhibiting element was previously mixed to a predetermined concentration.
A solder bath is formed by melting and filling a Cu-containing solder alloy into a solder bath. The solder bath is operated for about 1 to 2 weeks, and the reduction rate of the oxidation inhibiting element and the reduction rate of the solder bath are grasped.

The amount of decrease in the solder bath and the oxidation inhibiting element per a predetermined period is grasped, and the supply amount of the solder bath and the oxidation inhibiting element per the predetermined period is calculated for each. Obtaining the concentration of the oxidation inhibiting element in the solder alloy for supply,
A solder alloy containing an oxidation suppressing element at a concentration equal to or higher than the above concentration and having the same composition as the initial solder alloy except for the oxidation suppressing element and Cu is prepared. Of course, when the elution amount of Cu from the land or the like of the printed circuit board is small, a solder alloy containing Cu in an amount corresponding to the reduced amount of Cu from the solder bath may be prepared as the supply solder alloy. .

During the operation of the solder bath, the solder prepared in the above step is continuously supplied after the lapse of the predetermined period to prevent the concentration of the oxidation inhibiting element in the bath from decreasing to a certain concentration or less. Further modifications of the present invention include the following modes.

According to this aspect, when supplying the oxidation inhibiting element, the supply amount is determined in consideration of the decrease amount until the next supply. A solder bath is formed by melting and filling a solder alloy in which a predetermined concentration of an oxidation suppressing element is mixed in a solder bath.

The solder bath is operated for about 1 to 2 weeks, and the reduction rate of the oxidation inhibiting element and the reduction amount of the solder bath are grasped. By grasping the reduction amount of the oxidation inhibiting element and the reduction amount of the solder bath per a predetermined period, each supply amount in the period from this time to the next supply time is calculated. The concentration of the oxidation suppressing element in the supply solder alloy is determined and the supply solder alloy is prepared.

During the operation of the solder bath, the solder prepared in (1) is continuously supplied to keep the concentration of the oxidation inhibiting element in the bath within a certain range (it is always kept as close as possible to the concentration set in (3)). The present invention, as a simple method thereof, has a target concentration of about 2 to 6 of the oxidation inhibiting element concentration of the solder alloy for supply.
It is also possible to prepare a solder alloy containing double the concentration and supply it in an appropriate amount.

According to the present invention, as is clear from the above description, the oxidation suppressing element in the solder bath can be stably controlled. Although such effects have been explained mainly using flow soldering as an example, a method of soldering using a static solder bath in a high temperature environment of over 300 ° C, for example, soldering of urethane-coated copper wire Even in the method and the like, the consumption of the oxidation inhibiting element becomes remarkably large because the temperature of the molten solder becomes high. Therefore, even when the present invention is applied to such a soldering method, the effect is remarkable.

[0048]

[Example] (Example 1) In this example, P as the oxidation suppressing element
In the case of alloying and supplying at the same time.

The specific procedure of implementation is as follows. Sn-3.0Ag-0.5Cu-0.003P solder, which is a P-free lead-free solder alloy suitable for suppressing solder oxidation, is melt-filled in a solder bath to form a solder bath (mass: 330 kg).

The decrease amount of the solder bath in the solder bath after 12 days of operation, that is, the supply amount of the solder alloy and the decrease rate of the P concentration are calculated. Sn-3.0Ag-0.5Cu-0.003P Total amount of solder alloy supplied to the solder bath: 220 kg P concentration in the solder bath after 12 days of operation: 0% Decrease in oxidation inhibitor elements per day averaged over 12 days Grasp the amount, calculate the supply amount corresponding to each of these, set the concentration of P 2 in the supply solder alloy, and prepare the solder alloy.

Solder supply amount: 20 kg / day P Reduction amount: 2 g / day P concentration of the solder alloy for supply: 100 ppm Solder alloy for supply: Sn-3.0Ag-0.5Cu-0.01P Contains the solder bath of the initial composition 12 using solder bath
The printed circuit board was soldered for a day, and when the solder alloy in the solder bath decreased, the solder alloy: Sn-3.0Ag-0.5Cu-0.01P was supplied to the solder bath as needed. As a result of measuring the P concentration of the solder alloy in the solder bath on the 12th day, the P concentration was 0.
It was 003P%.

(Embodiment 2) This example shows a case where a Cu-free solder alloy is supplied as the supplied solder alloy.

Sn-3.0Ag-0.5Cu-0.003P solder, which is a P-free lead-free solder alloy suitable for suppressing the oxidation of the solder alloy, is melt-filled in a solder bath to form a solder bath (mass: 330 Kg).

The amount of decrease in the solder bath in the solder bath after 9 days of operation, that is, the supply amount of the solder alloy and the decrease rate of the P concentration are calculated. In this example, the composition of the supplied solder alloy is Sn
It was -3.0Ag.

Sn-3.0Ag-0.003P Total amount of solder alloy supplied to the solder bath: 90 kg P concentration in the solder bath after 9 days of operation: 0% Reduction in the amount of solder bath per day averaged over 9 days And the reduction amount of the oxidation inhibiting element is grasped, the respective supply amounts corresponding to these are calculated, the P concentration in the supply solder alloy is set, and the solder is produced.

Supply amount of solder: 10 kg / day P Reduction amount: 1.4 g / day P concentration of supply solder alloy: 170 ppm Supply solder alloy: Sn-3.0Ag-0.017P Solder tank containing a solder bath of initial composition Using 9
Solder the printed circuit board for a day, and supply solder alloy: S as needed when the solder alloy in the solder bath decreases.
n-3.0Ag-0.017P was supplied into the solder bath. As a result of measuring the P concentration of the solder alloy in the solder bath on the 9th day, the P concentration was
It was 0.003P%.

(Example 3) In this example, a Pb-containing solder alloy is supplied as the supply solder alloy. It is a P-containing solder alloy suitable for suppressing solder oxidation.
Pb-63Sn-0.003P solder is melted and filled in a solder bath to form a solder bath (mass: 330 Kg).

The amount of decrease in the solder bath in the solder bath after 14 days of operation, that is, the amount of supply of the solder alloy and the decreasing rate of P concentration are determined. In this example, the composition of the supplied solder alloy is Pb.
It was -63Sn.

Total amount of Pb-63Sn solder alloy supplied to the solder bath: 200 kg P concentration in the solder bath after operation for 14 days: 0.001% Amount of decrease in the solder bath per day averaged over 14 days and oxidation inhibiting element The amount of decrease in the supply solder alloy is calculated, the respective supply amounts corresponding to these are calculated, the concentration of P in the supply solder alloy is set, and the solder alloy is manufactured.

Supply amount of solder alloy: 20 kg / day P decrease amount: 0.9 g / day P concentration of supply solder alloy: 75 ppm Supply solder alloy: Pb-63Sn-0.0075P For 14 days using a solder bath of initial composition The printed circuit board was soldered, and when the solder alloy in the solder bath decreased, the supply solder alloy: Pb-63Sn-0.0075P was supplied to the solder bath at any time. As a result of measuring the P concentration of the solder alloy in the solder bath on the 14th day, the P concentration was 0.003 P%.

[0061]

As described above, according to the present invention, by stably controlling the oxidation inhibiting element in the solder bath, the oxidation inhibiting element in the solder bath is automatically kept constant during the normal daily work. It is possible to maintain permanent control of oxidation-inhibiting elements, which is maintained in the. According to the present invention, in order to avoid the disappearance of the oxidation inhibiting element of the solder bath and to permanently maintain the dross inhibiting effect, for example, the soldering quality in the flow soldering method can be stably ensured, which is an unprecedented advantage. It is effective. Further, the present invention is applied not only to the flow soldering method but also to the static soldering method and the like, and the same excellent operational effects are exhibited.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Haruo Suzuki             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Hirofumi Nogami             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Norihisa Eguchi             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Osamu Mougata             23 Senju-Hashidocho, Adachi-ku, Tokyo Senju Metal             Industry Co., Ltd. (72) Inventor Minoru Uejima             23 Senju-Hashidocho, Adachi-ku, Tokyo Senju Metal             Industry Co., Ltd. F-term (reference) 5E319 AA01 AC01 BB01 CC23 CD28                       CD51 GG03

Claims (4)

[Claims] 1. A soldering method performed using a solder bath to which an oxidation inhibiting element is added, wherein the oxidation inhibiting element has the same alloy composition as the alloy composition of the solder bath except the oxidation inhibiting element. Using a solder alloy containing as a solder alloy for supply; obtaining a reduction rate of the oxidation inhibiting element in the solder bath during the soldering operation; and a reduction amount of the oxidation inhibiting element that is consumed at the reduction rate or equal to that A solder alloy that supplies a larger amount of the oxidation suppressing element, is supplied to the solder bath as the supply solder alloy proceeds with the soldering operation; A soldering method characterized by performing soldering while controlling the concentration within a predetermined range. 2. A soldering method performed using a solder bath to which an oxidation suppressing element is added, wherein the solder alloy constituting the solder bath is a lead-free solder alloy containing copper as an alloy component; Other than the oxidation inhibiting element and copper, use a solder alloy having the same alloy composition as the alloy composition of the solder bath and containing the oxidation inhibiting element as a supply solder alloy; the oxidation in the solder bath during soldering work. Determining the rate of decrease of the inhibitory element;
Then, supplying the oxidation inhibiting element in an amount equal to or greater than the reduction amount of the oxidation inhibiting element consumed at the reduction rate, and supplying solder alloy containing or not containing copper,
With the progress of the soldering work as the supply solder alloy, supplying into the solder bath; consisting of performing the soldering while controlling the concentration of the oxidation inhibiting element in the solder bath within a predetermined range. Characteristic soldering method. 3. The oxidation inhibiting element in the supply solder alloy is contained in a concentration of 2 to 6 times the target concentration of the oxidation inhibiting element in the solder bath. Soldering method described in. 4. The soldering according to claim 1, wherein the oxidation inhibiting element is one or more elements selected from P, Ge, Ga and Ce. Method.